How would I go about controlling two elements two separate SSR on the same PID?
can someone point me in the right direction, is this possible?
Thanks,
Gus
Should these two elements be mutexed (not active at the same time)?
If that is not a concern, you can connect both SSRs to the same GPIO pin.
If the SSRs should be mutexed, then the cleanest solution is to have two PIDs with identical settings using the same setpoint, with the Digital Actuators mutexed, and the PWMs balanced.
I would like to have them come on at the same time, or be able to drop one after the mash hits strike temp, have only one maintain mash temp.
These elements are built into the bottom of the brewzilla. one relay turns on the 2000W the other relay turns on the 1000W and 500W. I can switch any of them off with the manual switch on the side.
I’m was hopping to use the one wire GPIO board for controlling the two elements.
I will connect both SSR to the same GPIO board channel for now.
This can be done by connecting the SSRs in parallel to the GPIO board pins. For the purposes of the controller, this all is just a single output.
This is somewhat trickier, not because it can’t be done, but because it will disrupt PID tuning. The PID settings are based on how quickly your heater will change mash temp. If you change this value by partially disabling your heater, your PID won’t function as well.
When the brewzilla turns on it turns one element on first then a few seconds later the other two elements. I thought maybe they were purposely doing this for in rush current. A resistive load should be consistent throughout so I think that’s irrelevant. I was just trying to make it behave similar thinking it might be easier on it’s board loading it not all at once.
If I was able to have two PID’s tuned differently. 1st PID tuned for both relay’s on at the same time . second PID tuned for only one element for running the Still. For this I would need them on separate GPIO. I would also need to mutex the PID’s so only one can be in operation at one time. Is there a chance a PID could turn on two GPIO pins at one time in the future?
Thanks,
Gus
You could use the Logic Actuator block to trigger the second Digital Actuator (and pin).
Thanks for the tip. I’ll look into this after work.
I think 2000 or 3000w won’t matter much for the pid. Especially when he turns it odd when stable state has been reached. It can cause a small blip, but the pid will adjust. I wouldn’t make it more complicated than needed and use a single pid.
I’m currently only using one output on the spark to control all element’s and the PID seems to be working fine. Does it matter that the brewzilla board uses mechanical relay’s? Will the PWM frequency be to fast at times? I was considering in modifying the circuit board and installing SSR instead.
Thanks,
There is a significant limit to the PWM frequency of mechanical relays. A relay will physically break after a number of operations. The (expected) lifetime number of operations depends on your relay. If you have a datasheet for the relays on your BrewZilla, you can find the information there.
Our PWM periods are already rather slow (seconds instead of the more typical miliseconds), and you can configure the PWM to have a longer period. This may be slow enough to reduce the wear and tear on the relay to acceptable levels.
In the end it depends: you know the period, and if you know the expected lifetime operations, you can calculate the expected lifetime of your relay while active. This may or may not be acceptable.